The problem is that there does need to be a middle ground. If they're legally liable there can be no rapid communication or large userbase because everything has to be reviewed by a person trusted by the site owner before it goes up. If they can't censor anything every platform that gets large enough to be worth advertising on looks like the inbox of the throwaway email you use to register for sketchy websites.
The middle ground is to have simple rules about 'no illegal content,' and then forums that are topical. If you don't want your site to be about politics, say that. If you want it to be about politics but not about other things, say so.
At the worst, do like this and many other sites have 'Keep threads on topic, politics go in the politics area, fiction discussion in the fiction area,' etc, etc.
This isn't rocket science, and as others have said, smaller more manageable platforms are a completely viable alternative as well.